Lumo comes with a set of icons that are designed to fit in with the default Lumo style.
The SVG sprites are used with the iron-icon element.
If you need to be in control of when or how iron-icon is imported, you may import iconset.html (instead of icons.html) to import only the icon definitions (iron-iconset-svg) without automatically importing the iron-icon element.
Use the icon size custom properties to set consistent sizes for all icons across your app. The Lumo icons are drawn on a 24×24 pixel canvas – the M size fits that by default.
You need to import sizing.html to use the sizing properties.